1. Field of the Invention
The present invention relates to a method for manufacturing a nitride semiconductor device that grows a multilayer film of a III-V group nitride semiconductor.
2. Description of the Related Art
A nitride semiconductor layer is generally formed on an inexpensive silicon substrate or sapphire substrate. However, a lattice constant of such a semiconductor substrate is greatly different from a lattice constant of a nitride semiconductor layer, and their thermal expansion coefficients are also different from each other. Therefore, high strain energy is generated in the nitride semiconductor layer formed on the semiconductor substrate by epitaxial growth. As a result, generation of cracks or a reduction in crystal quality is apt to occur in the nitride semiconductor layer.
To solve this problem, there has been suggested a method for arranging a buffer layer having stacked nitride semiconductor layers between a silicon substrate and a functional layer made of a nitride semiconductor (see, e.g., Patent Literature 1). To form this buffer layer, there has been adopted a method for fixing a flow rate of an ammonia (NH3) gas that is a raw material of a V group element and changing a flow rate of a raw material gas of a III group element. Therefore, a ratio of the V group element and the III group element is determined by a supply amount of the raw material gas of the III group element.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2008-218479